1. Field of the Invention
The present invention relates to an optical recording medium, and more particularly, to device and method for detecting a non-writable region of an optical recording medium.
2. Background of the Related Art
In general, in optical recording media which permit repeated rewriting without restriction, such as optical disks, there are Rewritable Compact Disc(CD-RW), Rewritable Digital Versatile Disc(DVD-RW, DVD-RAM, DVD+RW), and the like. The rewritable optical recording medium, particularly, the DVD-RAM is provided with a signal track having a land and a groove, and information is recorded on the land and the groove for increasing a recording density, respectively. And, for this, an optical pickup is provided with a writing/reading laser beam with a short wavelength, and an objective lens provided for collecting lights has a great numerical aperture for making the writing/reading laser beam smaller.
FIG. 1 illustrates a block diagram of a related art rewritable optical disk recording/reproducing device. The optical disk 101 has a land and a groove, for recording data on, and reading data from both of them.
An optical pickup 102 causes a beam collected by an objective lens to be focused onto a signal track of the optical disk 101 under the control of a servo controller 107, and directs a beam, reflected at a signal recording surface and collected by the objective lens, to an optical detector for detecting a focus error signal and a tracking error signal. The optical detector has a plurality of optical detecting elements, for providing an electrical signal proportional to an amount of light obtained from each optical element to a RF and servo error generator 105. As shown in FIG. 2, if the optical detector is divided into a specific number, i.e. four, in a signal track direction and a radial direction to have four optical detecting elements PDA, PDB, PDC, and PDD, the optical detector provides electrical signals a, b, c, d each proportional to an amount of light obtained in respective optical detecting elements PDA, PDB, PDC, and PDD to the RF and servo error generator 105. Then, the RF and servo error generator 105 combines the electrical signals a, b, c, and d to produce a read channel 1 signal required for data reading, a read channel 2 signal required for servo control, and a focus error signal FE, and the like. The read channel 1 signal is obtained by a+b+c+d, the read channel 2 signal is obtained by (a+b)−(c+d), and the tracking error signal TE is obtained by processing the read channel 2 signal. If it is a case when the optical detector is divided into two in the track direction, from a light amount balance of the two photodiodes I1 and I2, the read channel 1 signal(=I1+I2), and the read channel 2 signal(=I1−I2) is detected. That is, the (a+d) in FIG. 2 corresponds to I1, and the (b+c) in FIG. 2 corresponds to I2. The read channel 1 signal is provided to a data decoder 106 for reading, servo error signals, such as FE and TE, are provided to the servo controller 107, and a control signal for data writing is provided to an encoder 103. The encoder 103 encodes a data to be written into a writing pulse of a format required by the optical disk 101 and provides to an LD driver 104, and the LD driver 104 drives an LD in the optical pickup 102 in a power corresponding to the writing pulse, thereby writing the data on the optical disk 101. And, in reading the data written on the optical disk 101, the data decoder 106 restores an original form of the data from the read channel 1 signal detected form the RF and servo error generator 105. And, the servo controller 107 processes a focus error signal FE to provide a driving signal for focusing control to a focus servo driver 108, and processes a tracking error TE signal, to provide a driving signal for tracking control to a tracking servo driver 109. In this instance, the focus servo driver 108 drives the focus actuator in the optical pickup 102 to move the optical pickup 102 in up and down direction to follow the up and down movement of the optical disk 101 as the optical disk 101 is rotated. That is, the focus actuator for driving the objective lens, which collects lights, in a focusing axis maintains a distance between the objective lens and the optical disk 101 in response to a focus control signal. And, the tracking servo driver 109 drives a tracking actuator in the optical pickup 102, to shift the objective lens in the optical pickup 102 in a radial direction, for correcting a position of beam to follow the track.
In the meantime, in a case of the rewritable disk 101, as there is no information recorded on an initial disk, controlling and writing the disk is not possible. For this, disk tracks are provided to the land and the groove, information is written along the tracks, and control information for sector addresses, random access, rotation control and the like is written on the disk separately, to make tracking control available even for an empty disk having no information signal written thereon. The control information may be written in a header region by preformatting a header region at beginning of every sector. The header region pre-formatted at beginning of each sector is, in turn, provided with four header fields(header 1 field˜header 4 field). And, the header 1 and 2 fields and the header 3 and 4 fields are arranged to alternate the other with reference to the track center. FIG. 3 illustrates one example, wherein a header field structure for a first sector on one track is shown. However, the foregoing header structure has a bad influence in producing the servo error signal, such as a tracking error signal, and a focus error signal, actually. That is, the servo error signal read from the header region is distorted depending on a header structure, and is difficult to control. Therefore, in a case of DVD-RAM, in for generating, and making a stable control of a servo error, the servo error signal is held in controlling a servo in the header region for reducing an influence from the header. To do this, a method for identifying a header region is required, for which the read channel 2 signal is used in the related art.
That is, FIG. 4 illustrates a related art block diagram for detecting a header region, including an LPF(Low Pass Filter) 201 for receiving the read channel 2 signal and making low pass filtering, a first comparator 202 for providing an IP1 signal if the low pass filtered read channel 2 signal is higher than a preset slice level, a second comparator 203 for providing an IP2 signal if the low pass filtered read channel 2 signal is lower than the preset slice level, and a signal generator 204 for generating a header mask signal which represents a header region by using the IP1 and IP2 signal from the first and second comparators 202 and 203.
In the foregoing FIG. 4, the LPF 201 receives the read channel 2 signal from the RF and servo error generator 105, subjects to low pass filtering to produce a tracking error signal TE, and provides to the first and second comparators 202 and 203. As the header region, i.e., the header 1, 2 fields and the header 3, 4 fields are alternates with reference to a track center, the read channel 2 signal detected at the header 1, 2 fields and the header 3, 4 fields have phases(i.e., slopes) opposite to each other as shown in FIG. 5A. If such a read channel 2 signal in the header region passes through the LPF 201, the read channel 2 signal becomes a tracking error signal TE from which a noise is removed, as shown in FIG. 5. In this instance, as shown in FIG. 5C, if the tracking error signal TE provided to a plus terminal is higher than a slice level provided to a minus terminal, the first comparator 202 provides an IP1 signal, and, as shown in FIG. 5D, if the tracking error signal TE provided to the minus terminal is lower than the slice level provided to the plus terminal, the second comparator 203 provides an IP2 signal. Herein, it is assumed that a TZC(Tracking Zero Cross) position is set at the slice level.
In the meantime, phases of the IP1 and IP2 signals like FIGS. 5C and 5D differ depending on the track following at the present time being a land or groove. A sum of the IP1 and IP2 signals at the signal generator 204 produces the header region as shown in FIG. 5E. Therefore, respective servo error signals are held in the header region by using a signal as shown in FIG. 5E as a header mask signal which represents a header region, for reducing an influence from the header.
In the meantime, the read channel 2 signal as shown in FIG. 5A is one detected in a state the servos are stable, i.e., both the tracking servo and the focus servo are turned on. If it is a state the tracking servo is turned off, for example, either the traverse or the free running, when the servo is unstable, the IP1 or IP2 signal is not detected well, as well as the header region, too. In a traverse state which is mainly used in a seek, the tracking servo is turned off and the focus servo only is turned on, and the disk is rotated and the optical pickup is moved, for detecting the servo error signal. And, in the free running state which is mainly used for measuring an amount of eccentricity of the disk, the tracking servo is turned off and the focus servo only is turned on, and the disk is rotated and the optical pickup is fixed, for detecting a servo error. However, as described, if the header region is not detected properly, the servo error signal is affected by the header because the servo error signal can not be held at the header region. That is, provided that the IP1 and IP2 signals are produced from the read channel 2 signal, and used as signals for holding the header region, there are distortions occurred in servo error signals, such as focus error signal and tracking error signal, caused by a bad influence from the header in a traverse for seeking or in a free running for measurement of an amount of eccentricity.
FIG. 6A illustrates a read channel 2 signal detected from a data writable sector and a header region which informs a sector position, and FIG. 6B illustrates a TZC signal produced by slicing the read channel 2 signal at a TZC position, showing an example of the influence from the header.
Referring to FIG. 6A, the sinusoidal wave form is the read channel 2 signal detected at the data writable region, such as a sector, and the impulse form is the read channel 2 signal detected at a header region. As the header region is very short compared to the sector, a pulse width of the read channel 2 signal detected at the header region is significantly smaller than the same of the sector. In FIG. 6B, portions affected by the header are shown in circles. That is, the circled portions illustrate cases when detection of the header regions are not possible, with subsequent failure of holding the servo error signal, and occurrence of more pulses. In this instance, if a number of a TZC signal pulses are counted, a number of tracks passed can be known, permitting to know the present position of the optical pickup in a case of traverse, and to measure an amount of eccentricity of the disk in a case of free running.
However, the improper detection of the header region in the related art, that causes occurrence of more pulses of the TZC signal by the influence from the header as shown in FIG. 6B, results in the following problems.
First, the failure of holding the servo error signals, such as the tracking error or the focus error at the header region causes deterioration of a data quality in writing/reading.
Second, the more of pulses compared to a regular case in measurement of eccentricity leads to misunderstanding that the eccentricity is greater than fact, that gives a bad influence to the servos.
Third, because the optical pickup fails to reach to a desired position, the seek is slow and the servos are unstable. For example, though the optical pickup is required to advance 10 tracks, the optical pickup is misunderstood that the advance of 10 tracks is already made even if an advance of only 8 track is made due to the influence from the header, to stop movement of the optical pickup at the 8 tracks.
Fourth, though a tracking servo turn on should be made at a region other than the header region in a seek as the header region is a point disturbance comes in, the improper detection of the header region may leads to a tracking servo turn on at the header region, to cause the servo unstable, too.
Fifth, the lands and grooves are required to be switched for matching to a writing power, an offset and the like properly after the lands and grooves are determined as the lands and grooves have different recording powers, focus offsets, and tracking offsets, and opposite tracking error signals. If a number of the header are counted, the lands/grooves can be determined, and switching can be made. However, the improper detection of the header region in the related art impedes an exact switching of the lands/grooves.